This invention relates, in general, to ion implanters, and more particularly, to ion implanters with resolving apertures and shutters.
Ion implanters are able to implant ions in a controllable profile into a substrate. Ion implantation is a popular method for introducing dopant atoms into semiconductor and semi-insulating substrates during the manufacture of electronic devices. Ion implantation provides accurate dose control of chosen atomic species, and provides greater uniformity of dose across a semiconductor wafer.
Ion implanters include a source chamber in which gasses containing the desired atomic species are introduced and ionized. The ions are extracted from the source chamber in a beam by electromagnetic acceleration. The extracted ion beam then passes through an analyzing magnet that diverts ions selected by atomic mass from the extracted beam and redirects the selected ions on a second beam path. The ions in the second beam path are then accelerated towards a semiconductor substrate.
Some ion implanters include a shutter for controllably blocking the selected ions and additional discrimination of unwanted ions. The shutter serves to stop implantation when the semiconductor substrate has received a desired dose, and so is important for dose control. Unfortunately, conventional shutter structures allow a significant beam current leakage of selected ions to escape beyond the shutter even when the shutter is in an ion-blocking position.
Until recently, it was difficult to accurately measure this low level beam current leakage, and so manufacturers were not aware of its existence or significance. Shutter leakage causes significant dose variation. Moreover, even when the shutter is open, the desired ion beam current varies significantly due to beam current leakage past conventional aperture-shutter assemblies. A measure of this variation is referred to as beam stability. Beam stability also affects dose uniformity in the semiconductor wafer.
What is needed is a resolving beam shutter with significantly reduced leakage that provides improved beam stability and dose control for ion implantation.